Brown tastes good
We cook food to make it edible and safer to eat. During cooking the tissues of a food break apart, get softer and chewable, easier to digest, allowing more efficient absorption of nutrients. Additionally, cooking kills microorganisms that can be pathogenic. At the same time, cooking delivers a bonus, which is the incorporation of flavour into food. Cooked food tastes better than raw.
Why? What is happening during cooking and where all those complex flavours come from?
The answer lies to chemistry!
Cooking means mainly application of heat to food. Heat promotes the breakdown of chemical compounds and the formation of new, through many chemical reactions that take place much faster under high temperatures. One type of those processes are called browning reactions because they simply give rise to brown colourations on the food and are responsible for many of the tastes that foods develop during cooking.
Browning reactions can also take place without applying heat. These are a different story, are oxidation reactions mediated by the action of enzymes and result to unpleasant odours and textures (imagine the browning of an apple after leaving it cut on a board).
From the desired, heat-mediated browning reactions the most pronounced ones are caramelisation and the ‘Maillard reaction’.
Caramelisation is a complex, not-characterised process that involves the breakdown of sugars upon heating them higher than their melting point, that is for most of them >160°C, resulting to characteristic nutty, caramel-like flavours.
Maillard reaction kicks in at lower temperatures but still higher than the boiling point of water because it needs a dry environment to happen. It took its name from a French chemist, Louis Camille Maillard (1878-1936), that first described these events and involves the reaction between a simple sugar molecule and an amino acid that comes from the protein component of the food. Maillard reaction occurs widely and it is responsible for the characteristic aromas of baked, roasted and fried food.
The first step of the reaction involves a nucleophilic attack (1) of the amide group of the amino acid to the aldehyde group of the sugar with the subsequent production of a N-substituted glycosylamine. The latter is very unstable and through many rearrangements and subsequent cascade of reactions that are not completely characterised, gives rise to the production of numerous chemical compounds, the so-called melanoidins that are responsible for the brown colour and a palette of different tastes, flavours and aromas.
The types of aromas and flavours produced with the Maillard reaction depends on the amount of heat and on the types of sugars and amino acids present in the food; that’s why every food produces different tastes; bread tastes different than grilled stake or fish.
Until now all good, but things can go also bad. If the temperature rises higher than 180°C, color turns to black and that indicates food getting burned. This is due to the initiation of a different set of reactions, known as pyrolysis, that lead to the formation of compounds with carcinogenic properties.
To conclude, we are aiming to colour food golden brown and not black. However, the limit between the two is very subtle and here the skills of the cook come into play.
But can we enhance the Maillard reaction without burning the food, that means without raising the cooking temperature?
The answer is yes and lies again to chemistry and to chemical means that can speed up the initial step of the reaction, the nucleophilic substitution, which is also the rate-limiting step. For instance by enhancing even further the nucleophilic character of the amino acid, we could get more reaction going. This can be achieved by adding a base (2a). The latter attracts a hydrogen atom from the amino acid and thus constitutes the amide group negatively charged which translates to much higher ability to attack the electropositive carbon atom of the sugar’s aldehyde group. A common base that we use in kitchen is baking soda, chemically known as sodium bicarbonate or NaHCO3.
So the theory suggests that baking soda should speed up Maillard reaction thus giving faster and more intense the brown colour. But does it really works in practice? Lets check it out!
I tested this principle using bread as an example. I assembled a basic wheat bread dough and I shaped it to three bread rolls. Before putting them in the oven I left one roll untreated while I brushed the surfaces of the other two with increasing amounts of a baking soda water solution. I baked all the rolls together for the same amount of time and the result speaks by itself. More baking soda applied, browner the bread roll gets!
That sounds great and someone might think to just add loads of baking soda to get great taste. This won’t be exactly the case because should be also considered the taste of baking soda itself, which as a base it’s rather bitter (2b). That tells us once more that keeping a balance on doing something is usually the good way.
Basically this principle is being used to produce a typical snack bread in Germany, the infamous pretzel. These small breads with ring-like structures are having a distinct dark brown colour because before baked they underwent a short bath in a strong base solution; commonly used is food-grade sodium hydroxide (NaOH).
(1) Nucleophile is chemical entity that possesses free electrons and likes to donate them to an entity (electrophile) to form a bond in relation to a chemical reaction.
(2a) There are several definitions of a base but for the current example it fits more to say that base is a substance/molecule that accepts hydrogen ions (H+), known also as protons. The easier a base accepts protons the stronger it is. Base is the opposite of an acid that tends to release protons when in solution. In that sense base and acid are the opposite poles of a magnet with the difference that they like to react and neutralize each other. This neutralization or homeostasis is very important for life and living organisms function only under a certain acid-base balance.
(2b) Acids and bases have also tastes. Acids are the main contributors of the sour taste that in normal potency is pleasant and attractive. On the other side bases taste bitter and deliver a soapy feeling.
* This a revised version of the original post